Glass fibers are typically formed from attenuated streams of molten glass drawn through openings or nozzles in a metallic bushing. The bushing has a plurality of nozzles of predetermined dimension which correspond to the diameter of the glass fibers to be produced. The formation of nozzles in a bushing has been a costly, labor intensive and time-consuming endeavor, due in part to the exacting precision required to form nozzles which consistently meet stringent tolerance criteria on the order of .+-.0.25 millimeters (.+-.0.001 inches), relatively short bushing life and the metallurgical challenges of working with the precious metal materials of the bushing, such as directionally aligned dispersion strengthened or grain-stabilized metals.
K. Loewenstein, The Manufacturing Technology of Glass Fibres, (3d Ed. 1993) at pages 128-132 and (2d Ed. 1983) at pages 131-135 (each of which are hereby incorporated by reference) disclose four conventional methods for fabricating bushing plates. In the first method, a small indentation is created in a platinum alloy sheet. Drops of molten platinum alloy are deposited onto the apices of the indentation and shaped using a press. When an outer nozzle shape has been formed, the end of the nozzle is machined and a bore is drilled through the center of the nozzle to form the final nozzle shape.
In the second and fourth methods, holes are punched in the sheet at each nozzle position. Pre-manufactured nozzles are inserted into the holes and welded (for example by laser welding) to the sheet. If necessary, the center of each nozzle can be drilled and/or counterbored.
In the third method, coins or embossments are stamped on a side of a metal sheet and the sheet is annealed. The nozzles are then deep-drawn in two or three draws and annealed between each draw, if necessary.
The third method has been modified as disclosed in U.S. Pat. No. 5,173,096, in which the coined blisters or embossments are progressively punched with a series of punches which are shaped to progressively form nozzle tips. The tips of the nozzles are trimmed using an electrical discharge machining operation. U.S. Pat. No.5,140,732 discloses a similar method which further includes forming transitional channels in the surface of the sheet opposite the embossments prior to punching.
U.S. Pat. No. 4,292,862 at col. 3, lines 12-26 discloses a method of producing a stream feeder from a workpiece which is secured by applying pressure to the workpiece in the region to be punched and punching the workpiece with (1) a dome punch to form the general shape of the projection; (2) a lead punch to further define the shape of the projection; (3) a piercing punch to open the projection; and (4) a sizing punch to obtain the desired orifice shape.
Simplified, efficient methods and systems are needed which can consistently produce high quality bushing plates and in which a plurality of bushing plates can be formed from a single metallic plate to increase productivity and reduce cost.